Researchers from MIT’s Laboratory for Aviation and the Environment have
come out with some sobering new data on air pollution’s impact on
Americans’ health.

The group tracked ground-level emissions from
sources such as industrial smokestacks, vehicle tailpipes, marine and
rail operations, and commercial and residential heating throughout the
United States, and found that such air pollution causes about 200,000
early deaths each year. Emissions from road transportation are the most
significant contributor, causing 53,000 premature deaths, followed
closely by power generation, with 52,000.

In a state-by-state
analysis, the researchers found that California suffers the worst health
impacts from air pollution, with about 21,000 early deaths annually,
mostly attributed to road transportation and to commercial and
residential emissions from heating and cooking.

The researchers
also mapped local emissions in 5,695 U.S. cities, finding the highest
emissions-related mortality rate in Baltimore, where 130 out of every
100,000 residents likely die in a given year due to long-term exposure
to air pollution.

“In the past five to 10 years, the evidence
linking air-pollution exposure to risk of early death has really
solidified and gained scientific and political traction,” says Steven
Barrett, an assistant professor of aeronautics and astronautics at MIT.
“There’s a realization that air pollution is a major problem in any
city, and there’s a desire to do something about it.”

Barrett and his colleagues have published their results in the journal Atmospheric Environment.

Data divided

Barrett
says that a person who dies from an air pollution-related cause
typically dies about a decade earlier than he or she otherwise might
have. To determine the number of early deaths from air pollution, the
team first obtained emissions data from the Environmental Protection
Agency’s National Emissions Inventory, a catalog of emissions sources
nationwide. The researchers collected data from the year 2005, the most
recent data available at the time of the study.

They then divided
the data into six emissions sectors: electric power generation;
industry; commercial and residential sources; road transportation;
marine transportation; and rail transportation. Barrett’s team fed the
emissions data from all six sources into an air-quality simulation of
the impact of emissions on particles and gases in the atmosphere.

To
see where emissions had the greatest impact, they removed each sector
of interest from the simulation and observed the difference in pollutant
concentrations. The team then overlaid the resulting pollutant data on
population-density maps of the United States to observe which
populations were most exposed to pollution from each source.

Health impacts sector by sector

The
greatest number of emissions-related premature deaths came from road
transportation, with 53,000 early deaths per year attributed to exhaust
from the tailpipes of cars and trucks.

“It was surprising to me
just how significant road transportation was,” Barrett observes,
“especially when you imagine [that] coal-fired power stations are
burning relatively dirty fuel.”

One explanation may be that
vehicles tend to travel in populated areas, increasing large
populations’ pollution exposure, whereas power plants are generally
located far from most populations and their emissions are deposited at a
higher altitude.

Pollution from electricity generation still
accounted for 52,000 premature deaths annually. The largest impact was
seen in the east-central United States and in the Midwest: Eastern power
plants tend to use coal with higher sulfur content than Western plants.

Unsurprisingly, most premature deaths due to commercial and
residential pollution sources, such as heating and cooking emissions,
occurred in densely populated regions along the East and West coasts.
Pollution from industrial activities was highest in the Midwest, roughly
between Chicago and Detroit, as well as around Philadelphia, Atlanta
and Los Angeles. Industrial emissions also peaked along the Gulf Coast
region, possibly due to the proximity of the largest oil refineries in
the United States.

Southern California saw the largest health
impact from marine-derived pollution, such as from shipping and port
activities, with 3,500 related early deaths. Emissions-related deaths
from rail activities were comparatively slight, and spread uniformly
across the east-central part of the country and the Midwest.

While
the study is based on data from 2005, Barrett says the results are
likely representative of today’s pollution-related health risks.

Jonathan
Levy, a professor of environmental health at Boston University, says
Barrett’s calculations for the overall number of premature deaths
related to combustion emissions agree with similar conclusions by the
Environmental Protection Agency. The group’s results — particularly the
breakdown of emissions by state — provide valuable data in setting
future environmental policy, he says.

“A public-health burden of
this magnitude clearly requires significant policy attention,
especially since technologies are readily available to address a
significant fraction of these emissions,” says Levy, who was not
involved in the research. “We have certainly invested significant
societal resources to address far smaller impacts on public health.”